1. Field of the Invention
The present invention relates to a power converter system which is constituted by semiconductor power converter apparatuses each employing self-arc-suppressing semiconductor devices.
2. Description of the Related Art
As for the recent typical self-arc-suppressing semiconductor devices, there are Insulated Gate Bipolar Transistors (the so-called IGBTs) and Injection Enhanced Gate Transistors (the so-called IEGTs), both of which are classified as gate voltage driving semiconductor devices, and Gate Commutated Turn-off Thyristors (the so-called GCTs) which are classified as a gate current driving semiconductor device. In the case where such self-arc-suppressing semiconductor devices are accommodated together with diodes which are connected in anti-parallel therewith, in the same package, with a reverse conduction function, they are sometimes called reverse conduction power devices.
For example, with respect to the IEGTs, as described in EPE ""99-Lausanne xe2x80x9cHIGH POWER (4.5 kV, 4 kA turn off) IEGTxe2x80x9d, a plurality of IEGT chips and a plurality of diode chips can be accommodated in the same package to be used as one reverse conduction type power device. With respect to the IEGT having the collector current of 1.5 kA described in that article, the total number of chips which are accommodated in one package is 42, and these chips are broken down into the 30 IEGT chips and 12 diode chips.
In addition, in an article of TOSHIBA REVIEW Vol. 55, No. 7,2000 xe2x80x9cHigh-Power Device IEGTs For Power Electronicsxe2x80x9d, there is described an IEGT which has a collector current of 750 A and which is different in outside dimension of the package from the above-mentioned IEGT.
The total number of chips which are accommodated in one package is 21, and these chips are broken down into the 15 IEGT chips and the 6 diode chips. With respect to these chips, the total number of chips which are accommodated in the package is changed to make the collector currents different from one another. With respect to the semiconductor power converter apparatus employing the IEGT, a three-level inverter having a rated capacity of 8 MVA is described in an article of TOSHIBA REVIEW Vol. 55, No. 7,2000 xe2x80x9cHigh-Voltage Inverters Employing IEGTs for Industrial Motor Drivesxe2x80x9d.
On the other hand, with respect to the GCT, as described in an article of ABB REVIEW 5/1998 xe2x80x9cGIST-a new, emerging technology for high-power, low-cost invertersxe2x80x9d, the reverse conduction type power device in which the GCT region and the diode region are formed on the same silicon wafer and accommodated in one package has been realized as a product. In this article, the three GCTs are different in outside package dimension from one another. In this case, the area of the silicon wafer which is accommodated in the package is changed to change the controllable ON-current.
In addition, a power converter system, as shown in FIG. 15, a semiconductor power converter apparatus in which electric power is to be rectified, i.e., in a rectifier mode is larger than when the electric power is to be inverted, i.e., in an inverter mode, and a semiconductor power converter apparatus in which electric power is to be rectified is smaller than when the electric power is to be inverted, are connected in parallel with each other through a D.C. capacitor, is disclosed in JAPANESE PATENT APPLICATION LAID OPEN No. 288780 of 1986.
In this connection, the term forward-conversion means power conversion from A.C. to D.C., while the term reverse-conversion means power conversion from D.C. to A.C.
In FIG. 15, reference numeral 24 indicates a single-phase converter, reference numeral 25 indicates a three-phase inverter, reference numeral 26 indicates a D.C. capacitor, reference numeral 27 indicates a single-phase A.C. power source, and reference numeral 28 indicates an induction motor.
The two single-phase converters 24, which are connected in parallel with each other, are applied to a semiconductor power converter apparatus in which electric power to be rectified is larger than the electric power to be inverted, while the three-phase inverter 25 is applied to a semiconductor power converter apparatus in which the electric power to be rectified is smaller than the electric power is to be inverted. In addition, the two single-phase converters 24 and the three-phase inverter 25 are connected in parallel with each other through the D.C. capacitor 26, and the single-phase A.C. power source 27 is connected to an output terminal of the single-phase converter 24.
Also, an induction motor 28 for driving an electric railway system, for example, is connected to an output terminal of the three-phase inverter 25. When subjecting the induction motor 28 to the running power, the two single-phase converters 24 are operated in the forward conversion manner, while the three-phase inverter 25 is operated in the reverse conversion manner. In this case, the two single-phase inverters 24 need to input the driving electric power of the induction motor 28 and the electric power losses of all of the semiconductor power converter apparatuses 24 and 25 through the single-phase A.C. power source 27.
In addition, when subjecting the induction motor 28 to regenerative operation, the three-phase inverter 25 is operated in the forward conversion manner, while the two single-phase converters 24 are operated in the reverse conversion manner. The forward conversion electric power of the three-phase inverters 25 in the regenerative operation is necessarily reduced as compared with the forward conversion electric power of the single-phase converter 24 in the power operation. This results because there is electric power loss in the semiconductor power converter apparatuses 24 and 25, and electric power loss in the induction motor 28, and also the operating electric power is smaller than the regenerative operating power in the induction motor 28.
In the case where the conventional reverse conduction type power devices are accommodated in the package having the same fixed size, only the power devices, each of which has only the collector current or the controllable ON-current, are present. For example, in the IEGTs, the number of IEGT chips and the number of diode chips to the total number of chips is determined, and also in the GCTs, the occupancy ratio of the GCT region and the diode region to the total area of the silicon wafers is also determined.
Therefore, as long as the semiconductor power converter apparatus is constituted by using the reverse conduction type power devices having packages with the same electrode area, it may have the one and only forward convertable electric power and reverse convertable electric power. In other words, in order that the semiconductor power converter apparatus for forward conversion electric power and reverse convertable electric power, which are different from each other, may be constituted by using the conventional reverse conduction type power devices, the reverse conduction type power devices which are accommodated in the packages having different electrode areas and which are different in the collector current or the controllable ON-current from each other need to be applied to the semiconductor power converter apparatus.
In addition, since the reverse conduction power devices having different electrode areas must be cooled using different heat sinks or cooling fins, there arises the problem that it is impossible that the structures which are physically identical to one another are applied thereto to construct the semiconductor power converter apparatus, and hence the cost of the power converter system is increased.
In addition, in the case where the motor is driven by the semiconductor power converter apparatus employing the conventional reverse conduction type power devices, there arises the problem that the maximum capacity of the drivable motor is reduced.
This problem will now be described in detail while quoting the power converter system employed as adjustable speed driver for a motor having a configuration in which two three-phase semiconductor power converter apparatuses employing the reverse conduction type power devices having packages having the same electrode area are connected in parallel with each other through a D.C. capacitor, and one three-phase semiconductor power converter apparatus is connected to an A.C. power source, while the other three-phase semiconductor power converter apparatus is connected to the motor.
When the motor carries out the power running, the semiconductor power converter apparatus to which the A.C. power source is connected needs to, from the A.C. power source, forward-convert the total electric power of the electric power which is reverse-converted by the semiconductor power converter apparatus connected to the motor and the electric power loss of the two semiconductor power converter apparatuses to supply the resultant electric power. In this power running, regarding the conduction ratios of the self-arc-suppressing semiconductor devices and the diodes in the reverse conduction type power devices constituting the semiconductor power converter apparatus to which the motor is connected, it is understood that the self-arc-suppressing semiconductor device shows the larger conduction ratio. Also, regarding the conduction ratios of the self-arc-suppressing semiconductor devices and the diodes in the reverse conduction type power devices constituting the semiconductor power converter apparatus to which the A.C. power source is connected, it is understood that the diode shows the larger conduction ratio.
This can be inferred from that the semiconductor power converter apparatus having the A.C. power source connected thereto is placed in the running state near the forward conversion, i.e., the diode rectifier. The capacity of the motor which can be driven by the power converter system is limited by the forward-convertable electric power of the apparatus capacity of the semiconductor power converter apparatus connected to the A.C. power source.
Therefore, in the case where there is employed the reverse conduction type power device in which the occupation ratio of the conventional self-arc-suppressing semiconductor devices and the diodes is decided with respect to one package, there arises the problem that the capacity of the motor which can be driven in the adjustable speed manner is reduced.
As for the conventional method of solving that problem, there is the application of the circuit configuration in which the semiconductor power converter apparatus connected to the motor is made the three-phase configuration, and also the semiconductor power converter apparatus connected to the A.C. power source is made the single-phase configuration and are connected in the parallel multiplex manner. By the application of this circuit configuration, the forward-convertable electric power of the semiconductor power converter apparatus connected to the A.C. power source can be made larger than the reverse-convertable electric power of the semiconductor power converter apparatus connected to the motor because the minimum necessary number of reverse conduction type power devices is six with respect to the semiconductor power converter apparatus connected to the motor, while it is eight with respect to the semiconductor power converter apparatus connected to the A.C. power source.
In the prior art as described above, in addition to the problem that the number of reverse conduction type power devices used in the semiconductor power converter apparatus connected to the A.C. power source is increased as compared with the number of reverse conduction type power devices used in the semiconductor power converter apparatus connected to the motor, there arises the problem that since the semiconductor power converter apparatuses having the different circuit configurations must be employed, the same components and parts can not be applied to the semiconductor power converter apparatuses, and hence the cost required to manufacture the power converter system is increased.
In view of the foregoing, the present invention has been made in order to solve the above-mentioned problems associated with the prior art, and it is therefore an object of the present invention to provide a power converter system which is capable of making the forward conversion capacities and the reverse conversion capacities of a plurality of semiconductor power converter apparatuses connected to a D.C. capacitor different from one another, and of selecting a more suitable semiconductor power converter apparatus in accordance with each of the various loads, and also of reducing a product cost of the power converter system by making the circuit configurations identical to one another.
The present invention provides a power converter system which includes at least a plurality of semiconductor power converter apparatuses constituted by a D.C. capacitor and a plurality of power devices cooled by a cooling piece(s) having an output terminal connected to a load, and in which the plurality of semiconductor power converter apparatuses are connected in parallel with one another through the D.C. capacitor, the system being characterized in that each of the power devices includes as constituent elements self-arc-suppressing semiconductor devices and diodes each of which is connected in anti-parallel with the associated one of the self-arc-suppressing semiconductor devices; all of the semiconductor power converter apparatuses have the same circuit configuration; and the associated one of the power devices constituting at least one semiconductor power converter apparatus of the semiconductor power converter apparatuses connected to one another through the D.C. capacitor has the characteristics different from those of the other power devices constituting the other semiconductor power converter apparatuses.
In addition, the associated one of the power devices constituting at least one semiconductor power converter apparatus of the semiconductor power converter apparatuses connected to one another through the D.C. capacitor is accommodated in a package at least an electrode area of which is equal to that of each of the other power devices constituting the other semiconductor power converter apparatuses, and has the characteristics in which the quantity of generated heat is different therefrom when allowing the same current to flow therethrough.
In addition, the occupation ratio of the self-arc-suppressing semiconductor devices when the occupation area of the self-arc-suppressing semiconductor devices, and the diodes each of which is connected in anti-parallel with the associated one of the self-arc-suppressing semiconductor devices as the constituent elements of the associated one of the semiconductor power converter apparatuses connected to one another through the D.C. capacitor is decided as the overall occupation area is made different from that of each of the self-arc-suppressing semiconductor devices in the other semiconductors power converter apparatuses.
In addition, the occupation ratio of the self-arc-suppressing semiconductor devices of the associated one of the power devices which is applied to the semiconductor power converter apparatus having the forward-converted electric power larger than the reverse-converted electric power of the semiconductor power converter apparatuses is made smaller than that of the self-arc-suppressing semiconductor devices of the associated one of the power devices which is applied to the semiconductor power converter apparatus having the reverse connected electric power larger than the forward-converted electric power.
In addition, the semiconductor power converter apparatus, constituted by the power device having the smaller occupation ratio of the self-arc-suppressing semiconductor devices, of the semiconductor power converter apparatuses is connected to an A.C. power source, while the semiconductor power converter apparatus, constituted by the power device having the larger occupation ratio of the self-arc-suppressing semiconductor devices, of the semiconductor power converter apparatuses is connected to a motor.
In addition, the respective power devices have the same total number of chips in which a plurality of self-arc-suppressing semiconductor device chips and a plurality of diode chips are included as the constituent elements, and the occupation ratio of the number of self-arc-suppressing semiconductor device chips to the total number of chips of the self-arc-suppressing semiconductor device chips and the diode chips of the associated one of the power devices constituting at least one semiconductor power converter apparatus of the semiconductor power converter apparatus connected to one another through the D.C. capacitor is made different from that of the number of self-arc-suppressing semiconductor device chips in the other semiconductor power converter apparatuses.
In addition, the power devices have, on semiconductor wafers having the same area, regions of the self-arc-suppressing semiconductor devices, regions of the diodes, separation zones for separating the regions of the self-arc-suppressing semiconductors and the regions of the diodes from each other, and gate regions, respectively, and the occupation ratio of the region of the self-arc-suppressing semiconductor devices to the overall occupation area of the region of the self-arc-suppressing semiconductor devices of the associated one of the power devices constituting at least one semiconductor power converter apparatus of the semiconductor power converter apparatuses connected to one another through the D.C. capacitor and the region of the diodes is made different from the occupation ratio of the region of the self-arc-suppressing semiconductor devices in each of the other semiconductor power converter apparatuses.
Moreover, the self-arc-suppressing semiconductor device chip of the power device is either an Insulated Gate Bipolar Transistor or an Injection Enhanced Gate Transistor.
Moreover, the region of the self-arc-suppressing semiconductor devices of each of the power devices has a gate commutation type turn-off thyristor.
Moreover, the diode chip of each of the power devices is a silicon carbide diode chip.
Also, the power devices constituting at least a plurality of semiconductor power converter apparatuses are cooled by heat sinks or cooling fins having at least the same outer shape.